Maybe repost this with a more specific title?
I don't seem able to paste, but I've just found a very clear step by step guide after 30 seconds of googling.
Tell him to look at www.advicenow.org.uk
For the guide on child access without lawyers.
I would suggest that his first step is to think about why there are problems now. Is she just being difficult? Or is there a reason it's not working - e.g. If he's not committing to dates in advance, or if she doesn't want the boy missing an activity...
So he needs to think of what access he wants, and that is fair to his ex, and most importantly is in his son's best interests.
Then he needs to make sure he's squeaky clean on maintenance - is he? Not because it's part of the court access decision, but because it's the right thing to do.
I'd go in neutral "access isn't always easy, can we please agree a firm plan? I suggest what do you think?"
Only mention court if she won't agree, or agrees then breaks it. Then warn her.
If you don't use a lawyer, the costs aren't high. If he has a low income he can apply for help with court costs. "No way he can afford it" - this is the single most important thing he'll spend money on, so he should look to get his finances in order so that he can afford it.